1. Field
Apparatuses consistent with exemplary embodiments related to image communication, and more particularly, to removing chromatic aberration that occurs in an image generated by capturing a target subject.
2. Description of the Related Art
Recently, digital cameras have been improved with respect to technical aspects due to much demand and technical development. In particular, sensors have been improved with respect to a resolution aspect. However, the improved resolution causes aberration occurring due to a lens to be more recognizable. Particularly, chromatic aberration indicating incorrect color combination around an edge of an image is easily recognized, and thus, can be a problem. The chromatic aberration occurs if different wavelength components of light do not reach exactly at a focal surface of a camera because of a diffraction rate difference between the different wavelengths when light passes through a lens of the camera.
Depending on how the chromatic aberration occurs, the chromatic aberration may be classified into axial chromatic aberration and magnification chromatic aberration. As illustrated in FIG. 1A, the magnification chromatic aberration causes geometrical distortion of an image since a diffraction rate of light that passes through a lens 111 varies according to wavelengths of the light, such that focuses C1, C2, and C3 are formed at different positions with respect to an imaging surface 121, and thus, a size of the image varies according to channels. That is, a far edge portion of the image is greatly affected by the different diffraction rate, and thus, its defect level due to the magnification chromatic aberration is great. As illustrated in FIG. 1B, the axial chromatic aberration occurs since a diffraction rate of light that passes through a lens 111 varies according to wavelengths, and thus, distances between the lens 111 and focuses C1, C2, and C3 are different. As a result thereof, the axial chromatic aberration causes a blur since the focuses C1, C2, and C3 of different wavelengths do not match on the imaging surface 121. The aforementioned chromatic aberrations commonly cause a mismatch of edges of RGB channels, and thus, generate chromatic defects around the edges. In a digital image, purple fringing additionally occurs together with the defects due to the chromatic aberrations. The purple fringing indicates a phenomenon in which a purple color widely spreads over a region adjacent to a highly bright region. The phenomenon mainly occurs in an image obtained by using a charge coupled device (CCD) sensor rather than in an image obtained by using a complementary metal oxide semiconductor (CMOS) sensor, and occurs due to an effect of an ultraviolet ray incident on a sensor. Although a chromatic characteristic due to the phenomenon is similar to that of the chromatic aberrations, the phenomenon occurs in a wider region, and thus, it is difficult to efficiently remove the phenomenon by using a related art chromatic aberration removal technique.
In order to remove the chromatic characteristic due to the chromatic aberrations, most related art technologies perform correction by extracting representative coefficients of a lens, and then, changing an image size according to each channel. The related art technologies are divided into methods of previously extracting coefficients by using a pattern image, and methods of performing correction without an additional image. However, the methods do not consider a blur occurring due to the axial chromatic aberration and also do not consider the purple fringing, and thus, the methods may correct only defects occurring due to the magnification chromatic aberration. In order to complement such methods, recently, there are provided methods of removing the chromatic aberrations by performing filtering. The methods involve removing the chromatic aberrations by using a total sum of weights of pixels adjacent to a current pixel, and according to the methods, the chromatic aberrations are removed in a manner in which a weight of pixels that are greatly affected by the chromatic aberration is decreased, and a weight of pixels that are less affected by the chromatic aberration is increased. By doing so, not only the magnification chromatic aberration but also the axial chromatic aberration and the purple fringing are removed. However, due to limitation of the filtering, the chromatic aberration and the purple fringing are not effectively removed.